It's lights out at landmarks worldwide for Earth Hour on Saturday

More than a billion people around the world are expected to turn off their lights at 8:30 p.m. Saturday for Earth Hour 2013. The Opera House in Sydney, Australia, the Brandenburg Gate in Berlin and the Bird's Nest in Beijing will go dark too.

The annual global campaign has engaged more than 150 nations to voluntarily participate in the no-lights show this year.

The idea, of course, is to draw attention to climate change and the need to curb energy use. The event started in 2007 in Sydney. For time sticklers, each nation goes dark at 8:30 p.m. in its respective time zone; check Earth Hour's map to see which countries are participating.

In Los Angeles, the 100-foot LAX Gateway pylons at the airport will light solid green for an hour starting at 7:30 p.m. and then go dark between 8:30 and 9:30 p.m. The Las Vegas Strip, the Empire State Building and Rockefeller Center in New York also plan to douse the lights. On an individual level, the Girl Scouts of Greater Los Angeles on its website asks folks to turn off their electronic devices -- "No lights! No television! No computer!" -- for the hour.

But not everyone thinks this is a good idea. Bjorn Lomborg, a professor at Copenhagen Business School in Denmark, says in an Earth Hour essay that it sends the wrong message about how to tackle the world's energy woes.

"It may inspire virtuous feelings, but its vain symbolism reveals exactly what is wrong with today’s feel-good environmentalism," he writes. "Earth Hour teaches us that tackling global warming is easy. Yet, by switching off the lights, all we are doing is making it harder to see."